INBRED AND HYBRID ANIMALS AND THEIR VALUE 347 



It should also be borne in mind that some differences that have been 

 attributed to genetic causes may be due to parasites. Because of the limited 

 number of parents, there is a relatively high probability that an inbred line 

 will become uniformly infected, particularly with parasitic organisms 

 that are transmitted from mother to offspring. It is not impossible that 

 some mammary cancer differences between strains may be due partly to 

 this cause. 



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